Optical matrix switches are useful in optical communication networks wherein large quantities of data are transmitted through optical fibers at high speed. An output optical signal from one of the input optical fibers, each of which is connected to an optical matrix switch, can be supplied to a selective one of output optical fibers also connected to the switch.
Optical switching provides certain advantages over electronic switching techniques; and, oftentimes, optical matrix switches are utilized in electronic transmission lines by converting an electrical signal to an optical signal, passing the signal through the matrix switch and converting the optical signal back to an electronic signal. The advantages of utilizing an optical matrix switch include greatly increased band width and rapid switch configuration rates.
Spanke, U.S. Pat. No. 4,787,692, teaches optical switch networks and design rules for creating the same. The networks comprise a plurality of input and output stages of optical switch elements. Each input optical switch stage is comprised of a plurality of 1.times.2 optical switch elements, and each output stage is comprised of a plurality of 2.times.1 switch elements. The Spanke patent points out that with its invention utilizing such switch network and layout in interconnection, a non-blocking network is achieved having good signal to noise characteristics without crossover and crossthrough limitations as in prior art networks.
Suzuki, U.S. Pat. No. 4,822,124, represents an advancement to the matrix switch of the Spanke patent. As the Suzuki patent points out, with the conventional optical matrix switch, the size thereof is inevitably large in its longitudinal direction. Thus, for example, where the optical switch is provided with four inputs and four outputs to be called a "4.times.4 Optical Matrix Switch", four rows of optical switch elements must be included. Therefore, the longitudinal length cannot be less than a length as much as four times the longitudinal dimension of the optical switch element. In accord with the Suzuki patent, a stage of 2.times.2 optical switch elements is provided in place of two intermediate stages of 1.times.2 and 2.times.1 switch elements to thereby result in an optical switch smaller in the longitudinal direction.
Both prior art patents utilize switching elements based on a Ti-LiNbO.sub.3 substrate. The interconnection of stages of the input and output sections includes optical crossovers and crossthroughs diffused in the same substrate in which the switch elements are formed. The Suzuki patent indicates that, as a result, the substrate on which the four rows of optical switch elements are provided must be large in surface area, thereby substantially increasing fabric casing costs. With 2.times.2 group switch means in the center stage of a switching matrix, the total number of switches otherwise required is decreased, and consequently the number of optical crossover and crossthroughs is decreased. Thus, for example, in Spanke, a 4.times.4 matrix switch would be constructed using a stage 2 consisting of eight 1.times.2 switches, a stage 1 adjacent to input ports of four 1.times.2 switches, a stage 3 of eight 2.times.1 switches, and a stage four of four 2.times. 1 switches, each connected to an associated output port. With Suzuki, the total of sixteen switches in the intermediate stages 2 and 3 would be replaced by a total of four 2.times.2 switch means, thereby resulting in a matrix switch with a total of twelve switching elements. Again, as with Spanke, the switching elements are Ti-LiNbO.sub.3 substrate based switches.
The present invention takes advantage of advances in the fiber optics switching art. As pointed out above, both the Spanke and Suzuki patents utilize switching elements based on a Ti-LiNbO.sub.3 substrate. As both patents point out, with such switching elements, the longitudinal length of the matrix switch becomes critical. However, advances in the fiber optic switching art make possible the providing of discrete fiber optic switches which may be combined to form matrix switches wherein the longitudinal length is not of the criticality of matrix switches utilizing the substrate switches of the prior art. Further,
Application Ser. No. 07/520,350 teaches utilizing discrete fiber optic switches in matrix switches having switching elements arranged in a longitudinal configuration from input ports to output ports. Matrix switches of such configuration are improved in that connection between an input port and an output port may be made with an activation of a minimum number of switching elements. This not only decreases power requirements for the activation of matrix switches--which requirements may be substantial with switches having large numbers of input ports and output ports, for example, on the order of 64 input ports and 64 output ports--but further is advantageous in that, permitted, is a simplified and easier power switching arrangement for the connection of the optical matrix switch grid to the power controller.
Prior art matrix switches based on Ti-LiNbO.sub.3 substrate switching elements are further limited by the requirement that input ports and output ports be restricted to an even number of ports. Thus switches wherein the number of input ports is defined as N, and the number of output ports is defined as M, are characteristically limited to being non zero powers of 2. With the present invention, it has been found that discrete fiber optic switch elements may be provided having a 1.times.3 or 3.times.1 configuration thereby permitting matrix switches of an uneven number of input ports and/or an uneven number of output ports, and, in fact, any number of input ports and any number of output ports.
Switching elements useful in the matrix switches of the present invention are modifications of those taught by Gutterman, et al., U.S. Pat. No. 4,854,660, and Kokoshvill, U.S. Pending Application Serial Number 053,220, entitled "Fiber Optic Bypass Switch", filed on May 13, 1987, having European priority EP 0 299 604 A1. The switch elements of the matrix switches of the present invention include an imaging system having a symmetry such as a spherical reflector. The switch also includes a group of optical fiber end faces including at least a first optical fiber end face via which light is transmitted to the imaging system and at least a second end face which transmits light away from the imaging system. A displacing mechanism is provided for displacing the imaging system and the fiber end face group relative to one another between two positions. With a 1.times.2 switch element in a first position, the first and second fiber end faces are conjugate with respect to the symmetry of the imaging system so that light from the first fiber is imaged by the imaging system into the second fiber. In a second position, the first and third fiber end faces are conjugate with respect to the symmetry of the imaging system so that light from the first fiber is imaged by the imaging system into the third fiber. Thus, it is possible to switch the light from the first fiber into the second fiber or into the third fiber depending on the position of the displacing mechanism.
With a 2.times.1 switch element the first group includes two fiber end faces and the second group includes a single fiber end face designated third fiber end face. In the first position, the first and third fiber end faces are conjugate with respect to the symmetry of the imaging system so that light from the first fiber is imaged by the imaging system into the third fiber. In the second position, the second and third fiber end faces are conjugate with respect to the symmetry of the imaging systems so that light from the second fiber is imaged by the imaging system into the third fiber. Thus, it is possible to switch the light from either the first fiber or from the second fiber into the third fiber depending upon the position of the displacing mechanism.
Further, with modification of the switching elements taught by Gutterman, et al., U.S. Pat. No. 4,854,660 and Kokoshvill, Priority Number EP 0 299 604 A1, the displacing mechanism may displace both the imaging system and the fiber end groups relative to one another between four position whereby in a first stage, the imaging system is stationery and the fiber end face groups are switched between two positions and a second stage in which the fiber end face groups are stationery and the imaging system is displaced relative to the fiber end groups. Four relative positions may be provided making possible the providing of a 1.times.4 switch wherein in a first position, first and second fiber end faces are conjugate with respect to the symmetry of the imaging system so that light from the first fiber is imaged by the imaging system into the second fiber; in a second position, first and third fiber end faces are conjugate with respect to the symmetry of the imaging system, so that light from the first fiber is imaged by the imaging system into the third fiber; in a third position, the first and a fourth fiber end face are conjugate with respect to the symmetry of the imaging system so that light from the first fiber is imaged by the imaging system into the fourth fiber, and in a fourth position, the first and fifth fiber end faces are conjugate with respect to the symmetry of the imaging system so that light from the first fiber is imaged by the imaging system into the fifth fiber.
Interestingly, however, is that the fourth position may be avoided thereby eliminating a position whereby light from the first fiber would be imaged by the imaging system into the fifth fiber. And, further, the fifth fiber itself may be eliminated, thereby resulting in a switch with one input and three outputs. In this configuration, the switch includes a group of optical fiber end faces including at least a first optical fiber end face via which light is transmitted to the imaging system and at least second, third and fourth fiber end faces which transmits light away from the imaging system. The displacing mechanism not only displaces the imaging system relative to the fiber end face groups relative to one another but also may displace the fiber end face groups relative to the imaging system. In this instance, the mechanism may include two means, one for displacing the imaging system and a second for displacing the fiber groups. With the 1.times.3 switch element of the present invention in a first position, the first and second fiber end faces are conjugate with respect to the symmetry of the imaging system so that light from the first fiber is imaged by the imaging system into the second fiber. In a second position, the first and third fiber end faces are conjugate with respect to the symmetry of the imaging system so that light from the first fiber is imaged by the imaging system into the third fiber. In a third position, the first and fourth fiber end faces are conjugate with respect to the symmetry of the imaging system so that light from the first fiber is imaged by the imaging system into the fourth fiber. Thus, it is possible to switch light from the first fiber into the second fiber or into the third fiber or into the fourth fiber depending upon the position of the displacing mechanism. Thus, it is possible to switch the light from the first fiber into either the second fiber, the third fiber or the fourth fiber depending upon the position of the displacing mechanism.